Bel Canto REF600M Power Amplifier

A Class D Reference

Equipment report
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Solid-state power amplifiers
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Products:
Bel Canto Design REF600M
Bel Canto REF600M Power Amplifier

It may be hard to imagine, but when Bel Canto first opened its doors in 1994 the company made only tube-based electronics. The Bel Canto Orfeo SE2 power amplifier was a two-stage amplifier that used a triode input stage and one 845 triode output stage with local degenerative feedback and no global feedback. But in 1998, John Stronczer, Bel Canto’s chief designer, began to investigate switching amplifiers. “We began exploring linear switching Class D amplification in early 1998 with the goal of developing a more efficient, highly accurate, yet musical amplifier,” explains Stronczer. “We transitioned from our SET tube amplifiers to a technology that promised to offer superior performance over the long term. Our initial choice was from a company called Tripath.”

In 2000, Bel Canto introduced its first switching amplifier, as part of the Evo line that included both stereo and multichannel models. Within these designs Bel Canto implemented proprietary modifications to the original Tripath module and provided its own 50/60Hz power-supply architecture for main and auxiliary power supplies. The Evo line was in production for six years before the Tripath module was replaced by B&O’s ICEPower digital technology.

ICEPower offered lower-noise performance with even greater dynamic transparency due to its integrated switch-mode power-supply architecture. Stronczer designed and implemented external power filters and low-noise rectifiers as well as proprietary input stages in a compact, rigid chassis to improve the basic performance of the core ICEPower device. This technology was used in Bel Canto’s REF300M, REF1000M, and REF500M power amplifiers, which were in production for almost ten years.

Recently Bruno Putzeys developed new Class D NCore technology for Hypex. NCore uses an advanced, fully discrete, self-oscillating Class D architecture combined with a 5th-order control loop to achieve extremely low levels of noise and distortion throughout the audio bandwidth. A version of this NCore technology was chosen for application in Bel Canto’s current flagship Black power amplifiers, which were introduced in 2015—essentially a custom version of the NC1200 amplifier with the gain stage removed, replaced by a Bel Canto discrete gain stage.

The Bel Canto REF600M is the first amplifier in the REF series to use the NCore technology. According to John Stronczer, “There was a 10dB drop in noise going from Tripath to ICEPower. I’ve measured at least a 10dB drop in distortion, especially at high frequencies, going from ICEPower to NCore. Each 10dB represents a significant improvement in the technology. Noise also dropped by 3–6dB, (equal to 1.4x to 2x), reducing sonic artifacts and increasing musical detail and resolution.”

With its latest design Bel Canto claims to have achieved “the right balance between neutral transparency and musicality.” Stronczer says that the REF600M “demonstrates the full sonic promise that began to emerge over 15 years ago with the implementation of our first Class D amplifier.”

Description
The REF600M power amplifier, which can produce up to 300 watts into eight ohms, and 600 watts into 4 ohms, weighs only 15.4 pounds. Its half-size chassis is very similar to Bel Canto’s earlier eSeries amplifiers, but with a rounder and less squared-off faceplate. The back of the REF600M includes both single-ended and balanced connections along with a push-button selector, a pair of WBT “NextGen” five-way speaker connectors, a standard AC connection, and a 5-to-12 volt trigger connector. The REF600M comes from the factory set for 27dB of gain, but this can be changed to 33dB via an internal dip-switch.

The REF600M is based on Hypex’s NC500 OEM module and SMPS 1200 power supply. Bel Canto uses proprietary low-noise amplifiers with precision film resistors and capacitors to filter out high-frequency noise and prevent its aliasing within the audio band. The REF600M is also DC-coupled to avoid any dynamic degradation brought by coupling capacitors. According to Stronczer, “There is a lot of architectural similarity with the original Orfeo design and the REF600M. Both employ simple high-performance stages with local feedback and no global amplifier feedback. Also both have a first stage that provides most of the amplifier gain with a high input impedance and low output impedance to drive the output power stage.”

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